Currently, lateral double diffused MOSFETs (LDMOSFETs) and lateral insulated gate bipolar transistors (LIGBTs) are widely used in the circuits of logic power managers, electrical chargers, DC-DC converters or AC-DC convertors, etc. With the continuous shrinkage of the critical dimension of CMOS processes, in order to improve the efficiency and reduce the chip size of the LDMOSFETS and the LIGBTs, the on-resistance (Ron) of the LDMOSFETs and the LIGBTs should be as small as possible.
Further, with the continuous shrinkage of the critical dimension of the CMOS processes, the ability of the transistors for sustaining a high voltage and a high current continuously decreases. Deep sub-micron CMOS integration circuits (ICs) are more volatile to electrostatic charge (ESD); and easier to fail, thus the reliability of IC products may be reduced. In order to prevent the failure of the IC products caused by the ESD, ESD protection devices having a significantly good performance and an ability to sustain high voltage are used in the CMOS ICs. Currently, the ESD protection devices may include diodes, gate grounded NMOS transistors (GGNMOSFET), silicon controlled rectifiers (SCRs), LDMOSFETs, and LIGBTs, etc. In order to increase the safety of IC circuits, devices including LDMOSFETs and the LIGBTs, etc., may need to have a significantly large breakdown voltage.
For the LDMOSFETs and the LIGBTs, an on-resistance and a breakdown voltage are two important electrical parameters. The on-resistance is reversely proportional to a doping concentration of the drifting region; and the breakdown voltage is proportional to the doping concentration of the drifting region. That is, a higher doping concentration of the drifting region may aid to reduce the on-resistance of a LDMOSFET or a LIGBT and to increase an on-current of the LDMOSFET or the LIGBT, but it may reduce the breakdown voltage of the LDMOSFET or the LIGBT, which may affect the safety of the circuit. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.